UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a competitive ten-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a match where the techniques never quite clicked, with constant grabbing marring the action.
Two judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," the victor said in the ring as he was faced boos from the crowd.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the win but the contender endured the second setback of his 28-bout professional journey.
The Champion Claims Victory in Slow Match
His career development has plateaued in the past few years through management issues and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The audience's tolerance diminished because of frequent holding, with Parker going down various instances during clinches.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry battle to win the continental belt.
The stadium grew hushed for a profoundly moving homage ahead of the contest as ten bells sounded in remembrance of local hero Hatton, who passed away 46 years old in recently.
It was the first major televised fight night in the urban center since Hatton's passing. As the final chime disappeared, the quiet gave way to a chant of "there's just one Hatton".
The fighting during the bout matched the sentiment. The eventual winner was floored by a significant blow flush on the face in the early round, rising shakily to his footing on the eight count.
But the traditional red attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was injured quickly, noticeable damage forming under his face as the duo traded hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the decision with official scores of draw, 115-113 and 115-112, but the two athletes were persistent and brave, all the qualities their hero the legend stood for.
